Telephone system



March '371, l1931.

' H. TTzl.

TELEPHONE sysmm oi-iginal Filedl om., v14, 1927' Inuan or' MAN PatentedMar. 31, 1931 ED' STATES HANSYTATZL, oF VIENNA, AUSTRIA, Assienonf ToSIEMENS a' H-Ansx'u irxTIniver:senr-.-vv

PATENT oFF-ice SCHFT, OF WEBNERERK,v SIEIiIE1\TSSCIIA/DT,` NEAR BERLIN,GER'M'NY TELEPHONE SYSTEM:

Application tiledE October` 14', 1927?, Serial No..226,054, and inAustriay January 25, 1927; Renewed May 3, 1930.'

This invention relates to telephone systems in generaL-but is'concernedmore. particularly with calls between an automatic private' branchexchange and an automatic main exchange.

The object ofthe inventionis topermit a privat-e branch exchangesubscriber, after being connected! with a main exchange subscriber, tocall another local private branch subscriber and then reestablishconnection to the' established main exchange` connection without.releasing the'- main exchange connect-icm The oldest anrangements forthis obj ect pronideeach stationfwith two line connec-tions which,however, has the drawback t-'hatboththe set aslwell as the wiring systembecomes costly. Thereforait has been proposed toallot the means forbringing about the switching-over to the back\call',.not to thesubscriber, but tothe exchange line. By this it is madel possibleA thatonly one pair ofspeal-ingwines is necessary for the extension stat-ion.The enengization of the switchingv member: allotted; to thefcentralexchange line takes place mostly overalthird: wire or over earth, itYbeinga possible to give the impulse for switching: either permanently ortemporarily. In any case the call-back-set requires special devices.

rllhe present-invention: relates to acallbacksystem particularly forconnecting to automatic. house exchanges or private branch exchanges,wherein, for thel house sets, the exchange sets5, as Well as for thecall-fbael sets,t thef same simple type is usedi as is charactenisticfor ai system working according tot-he loopr system and theCalif-backdevice'fon private-branch exchanges for switching overtoa-bacl-call and also-for switching back totheY exchange call; isreleased by selecting' impulses or. by. a-4 similar operation;Preferably, af sequence switch carries out thenecessary switchingactions.

Fig; l: shows4 an example of' the invention andv indicatesv a system fonautomatic trafv fic. Qnly thoseY parts are shown which are essentialforan understanding of t-he. inventin:

The? automat-ichousef exchange will be assumedi as cateringfor 1,00()subscribers as a maximum'- The impulses are producedby interrupting theloop and the exchangelines are connected tothe top level' of the group.selectors so that the hunting selection off an exchange linetakes placethrough' the-group selector.V The centraly exchange. isassumedintheexample as being` an automatic exchange for-'10;OOO subscribers.y Thecall-back devices are, ofcourse, capable ofadaptation to eachexchange.`I

ln the first placca back call without-going trafiic will be described-The subscriberlA takes up=hisreceiver and' thereby in known, mannerengages agroup selector such as SEL over his preselector or line findersuch as' LS. By dialing ai par'- ticular number, for instance0,'t'hegroup selector SEL rises to the top level whereinv the officelines are connected.y After the runningdownl ofl the dial switchl thegroup selector commences to hunt for anidle exchange line".

The engragement of the'exchange line, i; e.,

the setvall'otted tothe exchange line, takes place'over thercfwire; Thetesting, relayy (not shown) ofthe group selector,haspotentiallyapplied'to it sothat if the groupiselector rests onv thecontact' plateof anidlev setV an testing circuit cany be tracedas follows: potential,testing relayof the4 group selector GWV, relay C' of the exchangeset'earth; The testing relay switches through the spealringzlined sothat, in the exchange set, the feed relay S70 may function, thusestablishing with its con; tact sp1 vthe loop to thecexchangef and forenergizing over contact S2911 a slowv acting relay V1. Thev relayl Cenergizes over' the above tracedcircuit and causes Itheenergization: ofrrelayv T over contact en. @ver contactcm'there functions a'relay-Xwhicliftakes care ofthe switching-through to the central exchange. 'llherelayl V'l is afsloW actingfrelay andy is-adjusted so that, during: therun# ning downy ofy the dial' switch, it does noteretract, even when itAisf short circuited by the retraction ofspil.

The subscribernow dials. and lets the dial switch rundown;consequently,the feed relay Sp receives the impulses andopens. the loopto theA exchangev throughgthecontact sp1 a correspondingnumbervofvtimes. During the first retraction of the impulse relay Sp, therelay V2 responds in known manner, this also being provided with delayedretraction and the following circuit is established: potential overretracted contact apn, relay V2, contact o1 III, earth. In order toimprove the impulses the relay V2 short circuits the choke Drl in theexchange loop over contact o2 I. At the exchange set there is a sequenceswitch St, which is advanced a step each time the relay V2 operates. Inthe present case the dial switch is operated four times to send fourseries of impulses to complete a connection. The sequence switch St hasthus been advanced by four steps until it finds itself in a positionwhich may be defined by exchange speaking. In this position the relay Fresponds over: potential, rotating arm 2 of the sequence switch Stcontact V2 IV, relay F (winding II), contact o1 III earth. rIhe loopover the main exchange trunkline for holding the main exchange switchesnow extends by way of contacts fu and choke coil D112. IJVhen the calledsubscriber A replies, both subscribers are in connection with eachother.

In order to maintain a back call within the house, the house subscriberhas to advance the sequence switch St by a further step, for whichpurpose he has to dial once and allow the dial to run down. Preferablyonly one impulse is given out of course. During the ruiming down of thedial switch, as already mentioned the relay V2 responds, and overcontact v2 II advances the sequence switch St the required step.

After the retraction of the relay V2 a circuit for the switching relay Uis formed as follows: potential, rotary arm 2 of the sequence switch St,contact o2 III, relay U, back contacts LH, o1 III, earth. 'Ihe relay Uholds itself over contact um; it is provided with a slow-actingretraction. Through contact un the relay X is made to retract andthereby brings about the switching of the impulse contact sp1 to theback call terminal. By the opening of the contacts mi and wm theexchange subscriber A is cut off but his loop is still held over thecontact u, and choke coil IN2.

The house subscriber A now hears the Vdial toneof the automatic houseexchange, and dials the telephone number of subscriber A2 with whom hewishes to conduct the back call. In the present case the housesubscriber A2 is to be selected by a three-digit number. The sequenceswitch is therefore advanced three rotary steps by the time the localswitches such as SEL and CONN have completed connections to the line ofsubscriber A2. In order to return to the main exchange connection, thesequence switch must be advanced again by one step, which may be done bydialing the number l once more.

In order to permit several back calls to be made, it is necessary toagain return the sequence switch into the position exchange speaking.This is done in the following manner. As is mentioned, the relay Uretracts with a slow action and tierefore it keeps its contact um closedfor a moment, even when the rotary arm 2 of the sequence switch hasalready left the contact plate. Now a temporary circuit for a relay I-Iis closed; potential, rotating arm 2 ofthe sequence switch St, relayI-I, contacts un, hu, o, III, earth. The relay I-I holds itself over itscontact 7am, and connects the rotary magnet DM of the sequence switch Stto a relay interrupter RU so that the sequence switch St is rapidlyadvanced until the arm of the same comes into the position exchangespeaking. In this moment the relay II retracts and stops the rotaryswitch. rIhe exchange call can now be continued. As the positionexchange speaking agrees perfectly with t-he condition before the backcall was made, any number of such calls may be made.

Incoming trafic rIhe alternating ringing current from the exchangeenergizes the calling relay A which holds itself over its winding II andswitches on the calling lamp AL. The operator at the private branchexchange operates her listening key allotted to the exchange line in theposition central oliice, whereby the operators set is connected in knownmanner to the exchange line and the relay F is encrgized over winding I.The requirements of the calling main exchange subscriber, such as A',are attended to by means of a plug S and jack .I when a call to a localprivate branch subscribers line, such A, is made thereby. rIhe jacksleeve of the private branch exchano'e has a potential so that the relayK can respond over the c-wire of the plug S and at the same time, byshort circuiting its high resistance winding II, makes the calledsubscribers line busy in a well known manner.

lVhen the called subscriber A replies the line relay Sp responds overthe loop circuit formed by raising the receiver, and atcontact spl againcloses the loop to the exchange, because through contact 751, the relayX, which initiated the switching-through to the exchange, is alreadyenergized. Line relay SP at contact SI)II again causes the energizationof relay VI. The response of the relay Vl causes a circuit to be formedfor the relay II as follows potential, rotary arm 2 of the sequenceswitch St, position O, relay I-I, contact 761, o1 III, earth. The rela-yII over contact hn again connects the rotary magnet DM of the sequenceswitch S' to the relay interrupter RU. The sequence switch rotates inthe manner previously described to exchange speaking position. At thismoment, asal-V ready described for the outgoing traiiic, the relay Fresponds over winding II and again Iwas described forl outgoing trailc.

igvesgsea' The switching over to" a back callnervi talesf place-inexactly the samemanner as The housesubscriberA first dials digit No: 1land: then the number of the desired house subscriber Whom he:Wishestocall, At the end ofthegconversation'the-returntothe-exchangecall is again made by selecting dialingj digit No: Vl, whereby thesequence switch is once moresent1 into the position exchangespeaking byYmeans of the relay interruptor.l

Release of acaZZ When thev house subscriben A hangs up hisreceiver thefeed relay S39 retracts and overcontactspn temporarily'energizes therelay V2, short circuiting, Withfthe samecontactf, therelay V1', whichretracts with a delayed motion thereby interruptingalso the circuit forthe relayV'g. Through contact nl I the relay interrupter LUI isconnectedover the rotaryarmA l ofthe sequence switch St-to the rotarymagnet DM Which, inknovvn manner is sent into the 0 position or itsnormal'i position; The Winding III of the relayIl"lies'iirparallel withtherotary magnet DNI; If the call Was an outgoing one therelayy C' wouldbe short circuited by the retraction of4 the contact o1 II ofthe relayVl and therebytheo-Wire to the groupV selector Wouldbeinterrupted, thuscausing release. rSincetherelay T remains energized until thesequenceswitch has returned to the 0 position, the exchange set'remainsl blocked toaresh-calljustv aslong. I' thecall, hon ever, is anincoming-- one, the clearing lamp islit and-the operatorhas-to Withdrawthe plug.y

lVhen connect-ion is made to a manual exchangeit is desirable atl theend of a call, further vto block-'the line for about l5Y seconds for theoutgoing traic, in order that the central exchange operator mayhave timeto cutoff-"the connection; For this purpose also theA sequencelsn'itchSt may be used; until\v the returnftotheO'position is-eiected by aslon7`actinginterrupter- LU. Since the relay' T re1nainsenergizedjust aslongover `its Winding vIII", thedesired'blocking of the exchangeline-isachieved;

What is-claimed is:

l1. In an automatic telephone system, a privateebranoh exchange, a mainexchange, a two-Wire trunkcircuit connecting said exchanges, means forvestablishing aA talking connection over said trunk circuiti in eitherdirection,y means controlled by a calling subscriber` in the privatebranch exchange dialling apredetermined number of digits after beinglconnected toV a main exchange-subscriberand Without hanging up hisvreceiver orholdingthe connection to the mainY exchange subscriber andfor completing afconnectiontoia desi'ned local priivatebranchi exchangesubscriber.; saidmainiexchangesub scriber' being excluded. from thetalking cir.-l cuit' of: the'la'st mentioned. completed connectionbetween thelocalf subscribers', andmeans responsive to a-isubsequentfdialling openafV tiionwithout the calling subscriber hangingup: his receiver for.' disconnectiingv said other. local subscriben andifor again connecting with said!establishediconnection to said. mainexchange subscribers line.. a

2. In a private branch` exchange,l a.tWo.- Wire trunk circuit: extendingto a main exchange, meanscontrolledv by: a calling; subs scriber. forestablishing a talking connection over said" trun'kicircuit to: asubscriber 'ine the main exchange, aisvvitchinsaiditrunkv circuitoperated! oneistep .foreach digitoi 'the called number and? seti in4main. exchange speaking position at they end; off the. digitimpulses,means responsive to;l subsequentimpulsessent by thev calling subscriberfor. moving/'said switch out ot speaking posit-ion',.for holding. theestablished; connection to: themain: ex-V change subscriber., and*` Vforcompleting: a talking connection. to another local? privatebranchexchange subscribersline,andmeans responsive to a further:subsequent impulse sentby the calling` subscriben for disconnecting saidother localsubscniber, .fori reconnect,- ing' with. said'. establishedconnection to the main: exchange subscribers: line,.l and forautomatically causingsaidI switch toVV again step to exchange talking;position.

3; Iny a. private branch exchange, a tivos Wire trunk' circuitextendingto' amain ex-A change, means` controlled by;y a calling; subscriben for establishingfa talking; connection over said tnunkicircuitto a: subscriber inthe main exchange; ai switchl in. said trunk ciricuitoperated' one.f step; for; each .digitV ofv the called number andl set:ini main: exchange speaking `positional: thefend` o'the digit-im,pulses-means respoi'isivetol subsequent in,- pul'ses fsent byY thercallingsubscriber for movingsaidlswitchloutof speakingpositiomionholding the. established` connection-to the main. exchange subscriber,`andxfonf completingVL atalkingrconnection to another. local pri; vatebranch exchangev subscribersrline, and means responsive to furthersubsequent impulse sent by the: calling i subscrriberft'or' disconnecting saidV othen local' subscriber, for reconnecting:With-saidrest ablishetl .connection to the main exchangesubscribensline, and for' automatically: causingi said? switchto againstep to'exchangeftalking position, and means,- controlledaby' said*switchzfor momenh tarily` maintaining said trunk: circuit busy after'the'- release. ofthe-5 establishedI connec; tion.v

46. In a private branch exchange, artwo Wirey trunk circuit extending to@a2 main ex; change, andi' means-insaid trunkf circuit to enable a Vcallingfprivate branch exchange subscriber to, iirst, call a mainexchange subscriber, second, complete a connection to another privatebranch exchange subscriber without releasing the connection to the mainexchange subscriber, and, third, release the connection to the saidother local private branch exchange subscriber and reconnect to theestablished connection to the main `exchange subscriber, said meansbeing controlled by the calling private exchange subscriber diallingpredetermined digits without hanging up his receiver.

5. In a private branch exchange, a two wire trunk circuit extending to amain exchange, and means in said trunk circuit to enable a callingprivate branch exchange subscriber to, iirst, call a main exchangesubscriber, second, complete'a connection to another local privatebranch exchange subscriber without releasing the connection to the mainexchange subscriber, and, third, release the connection to the saidother local private branch exchange subscriber and reconnect to theestablished connection to the main exchange subscriber, said meanscomprising a sequence switch in said trunk circuit which is directivelycontrolled by impulses generated by the calling subscriber.

6. In an automatic telephone system, a trunk line having two branches,means in said trunk line responsive to its seizure for closing a bridgeacross said trunk line, means responsive to impulses transmitted by acalling subscriber for interrupting said bridge to operate a train ofautomatic switches over the iirst of said branches to complete aconnection to a called line, and means responsive to subsequent impulsestransmitted by said calling subscriber for disconnecting said firstbranch from said trunk line, for holding said switches inoperated'position over said first branch, for connecting said trunk lineto the second of said branches, and for interrupting said bridge tooperate a second train ci' automatic switches over said secondbranch tocomplete a connection from said calling'line to a. second called line. y

7. In an automatic telephone system, a trunk line having two branches,means in said trunk line responsive to its seizure for closing a bridgeacross said trunk line, means responsive to impulses transmitted by acalling subscriber for interrupting said bridge to operate a vtrain ofautomatic switches over the iirst of said branches to complete. aconnection to a called line, means'responsive to subsequent impulsestransmitted by said calling subscriber for disconnecting said firstbranch from said trunk line for holding said switches in operatedposition over said iirst branch, for connecting said trunk line to thesecond of said branches, and for interrupting said bridge to operate asecond train of automatic switches over said second branclrto complete aconnection from said calling line to a second called line, and meansresponsive to further impulses transmitted by the calling subscriber fordisconnecting said second branch from said trunk line thereby releasingthe second switch train and for reconnecting said trunk line to saidiirst branch and said first called line.' i

8. In an automatic telephone system, a

trrmk line, means controlled by a calling subscriber for operating atrain of automatic switches over the two conductors of said trunk linein series to complete a connection to a called line, and meansresponsive to said calling subscriber dialling a predetermined numberfor opening both conductors of said trunk line and for closing a bridgeacross said conductors at a point beyond the opened section in order tohold said train of switches in operated position. 9. In an automatictelephone system, a trunk line, means controlled by a calling subscriberfor operating a train of automatic switches over the two conductors ofsaid trunk line in series to complete a connection to a called line,means responsive to said calling subscriber dialling a predeterminednumber for opening both conductors of said trunk line and for closing abridge across the conductors of the outgoing section in order to holdsaid train of switches in operated position, and a second train ofautomatic switches controlled over the conductors of the other sectionto complete a connection from said calling line Vto a second called lineresponsive to said dialling operation.

10. In an automatic-telephone system, a trunk line, means controlled bya calling subscriber for operating a train of automatic switches overthe two conductors of said trunk line in series to complete a connectionto a called line, means responsive to said calling subscriber dialling apredetermined number for opening both conductors of said trunk line andfor closing a bridge across the conductors of the outgoing section inorderto hold said train of switches in operated position, a second trainof automatic-switches controlled over the conductors of the othersection to complete a connection from said calling line to a secondcalled line responsive to said dialling operation, and means responsiveto a subsequentdialling operation-by said calling subscriber fordisconnecting and releasing said second train of switches from theconductors of said other section and for reconnecting said conductors tosaid iirst train of switches. l

il. In a telephone system, a trunk line having two branches, meanscontrolled by a calling subscriber over the first of said branches foroperating atrain of switches to complete a connection to a called line,and means responsive to a dialling operation by said calling subscriberfor operating a second train of switches over the second of saidbranches to ifa-98,507

15 `completeaconnectionffrom said-calling line `to la second calledline, and or disconnecting .the irstbranch from said trunk line Without.releasing said connection tothe iirst called line du-ring the timey the,connection to Vsaid -zosecond called iline `is maintained, and .meansrespon-sive to a `subsequent dialling operation by said calling.subscriber for disconnecting and releasing the connection 4to Ythesecond .called :line -overthe second .branch `and for reconnecting the:calling line .to .said irst cal-led rlineconnection over the .firstbranch.

-1-3. In an automatic telephone system, a 'private branch exchange, Vamain exchange, :a trunk 5line connecting said fexchanges, means 30controlled by a -calling branch exchangesub` ,scriber for completing aconnectionoversaid ytrunk line .to :a main .exchange Vsubscribers line,means controlled by said callin subscriber ldialling a predetermined.num er of digits without hanging up his .receiver for disconnecting-butnot releasing the1connec'tion 'to-theanain exchange subscriberanddorzcoinvpleting -a .connection vtoa .desired ylocal .private.ibranchlexcharn'ge subscriber@ line.

14,-. In v.an automatic .telephone system, a private branch exchange, amain exchange, a trunk l.line Kconnecting said exchanges, meanscontrolled .by acallingbranch exchange sub- .soriber for completingaconnection vover said Strunk fline to a .main exchange subscribers.li-ine, means controlled by said .calling subscriber dialling .a'predetermined number of digits Without hanging uphis-.receiverfordisconnecting but notreleasing theconnection to .50

,pleting a connection .to a desired local 1private branch exchangesubscribers line, and means 4responsive to asubsequent `diallingoperation ofsaidcalling subscriber without hanging up 1his receiver fordisconnecting vand releasing l the Iconnection to .said .other localsubscribers lineland for connecting .the calling line to said.established connection .to the .main exchange .-subscriberis line.

15. In fan .automatic telephone system, a .trunk line, meanscontrolledby acalling sub- .scriber over said tru-nk .line for .operating a trainof automatic switches to complete a connection to :afcalled line, means.responsive to T fsaid .calling ysubscriber dialling a ,predeter- -themain yexchange :subscriber and .for comminednumber for operatinga.secondtrainof .automatic switches over said .trunk line Yto complete aconnection ,from said-foalling-line `to 1 -second called line, .and.means whereby ysaid iirstand second'tra.in-of:switches aredis-.connected .from .eachiothei'and the .first .train is A*maintained `in`operated position.

16. In l.an automatic `telephone system, .a

/tiunkline, meanscontrolled by aicallingsubvscii'ber over .said trunkyline for voperating `a ytrainof automatic switcaes .to complete aconinection Yto a .called line, .mea-ns v`responsive .to ysaid `callingsubscriber dia-lling .a `predeter- -min-ed number for operating .a`second train yof automatic switches -over .said trunk iline to completea connection ifrom ,said Acalling line to a .second called line, meanswhereby said -rst and .second train of .switchesare disconnected :fromeach other .and the :first -train is maintained iii-operatedpositionyandmeans responsive toa subsequentdialling.op-

eration by :the .calling .subscriber for `disconnecting ,and releasingthe lconne'ction .to Vthe second called lline and .fior reconnecting.said

Icalling .line .to the ,first `sW-itch atrain.

-17 In .a telephone rsystein, vla .main fexchange, aprivateebranchexchangeaa two Way trunk line :connecting said exchanges,uneans Y for vcompleting a. connection :between .a .main

exchange subscriberis line and a ,private branch exchange subscriber@fline in either direction over said trunk line, and means responsive to.a .dialling operation by the '.pr-ivate branch subscriber regardless ofwhether such subscriber :is :the ica-lling yor the called subscriber inthe established connection for disconnecting the branchexchangesubscribers line from the main exchange Tsubscribers line Withoutreleasing 'the connection thereto and for completing a connection:ti-tom ,theV

.private branch -subsoribers :line xto ra .second called line.

18. In sa telephone' system, a main exchange, 5a gprivate branchlexchange, a two Way trunk .line connecting :said exchanges, ymeans forcompleting a connection between a :main exchange subscribers line and aaprivate branch exchange subscribers ,line iin either Vdirection roverlsaid trunk line, .means responsive to a *diatllingvoperation byythe-private branch subscriberregardless of Whether Vsuch subscriber Visthe calling or the -called subscriber in the establishedconnection for-quent dialling opera-tion by `said private branch subscriber erdisconnecting andreleas-ing the connection to ,the .second called linea-nd for reconnecting the ,private branch subscriber to ythe establishedconnection to lthe mnexchan-ge subscriberis line.

19. In a private branch exchange, a trunk line extending to a mainexchange, means controlled by a calling subscriber for establishing atalking connection over said trunk line to a subscriber in the mainexchange, a register in said trunk line operated one step for each digitof the called main exchange subscribers number, and means responsive tosubsequent impulses transmitted by the calling subscriber for operatingsaid register to disconnect the calling subscribers line from theestablished connection to the main exchange without releasing suchconnection and for completing a connection between said calling line anda second called line over a branch of said trunk line.

20. In a private branch exchange, a trunk line extending to a mainexchange, means controlled by a calling subscriber for establishing atalking connection over said trunk line to a subscriber in the mainexchange, a register in said trunk line operated one step for each digitof the called main exchange subscribers number, means responsive tosubsequent impulses transmitted by the calling subscriber for operatingsaid register to disconnect the callingsubscribers line from theestablished connection to the main exchange without releasing suchconnection and for completing a connection between said calling line anda second called line over a branch of said trunk line, and meansthereafter controlled by said register responsive to a subsequent digitfor disconnecting and releasing the connection to the second called lineand for reconnecting said calling line to the established connection tothe main exchange subscribers line.

21. In a telephone system, a trunk line having two branches, meansresponsive to impulses transmitted to sai-d trunk linel for completing aconnection from a Acalling line to a called line overthe first of saidbranches, a register associated with said trunk line operated one stepfor each series of impulses transmitted to said trunk line, and meanscontrolled by said register after taking a predetermined number of stepsfor switching the trunk line from connection with said irst branch toconnection with the second of said branches in order to completev aconnection from said calling line to a second called line.

22. In a telephone system, a branch exchange in which outgoing trunkconnections are completed by means of automatic switches directivelycontrolled by a branch exchange subscriber, and in which incoming trunkconnections are completed by an attendant, means responsive to directiveimpulses transmitted by a branch exchange subscriber en- 1 gaged ineither' an incoming or outgoing vtrunk connection for establishing anauxiliary connection to another branch exchange subscriber withoutreleasing the trunk connection, and means responsive to furtherdirective impulses transmitted by the branch exchange subscriber forreleasing said auxiliary connection and for reestablishing the trunkconnection.

23. InV a telephone system, a branch exchange in which outgoing trunkconnections to main-exchange subscribers are completed by means ofautomatic switches directively controlled by a branch-exchangesubscriber and in which incoming trunk connections from main-exchangesubscribers are completed by an attendant, means responsive to directiveimpulses transmitted by a branchexchange subscriber engaged in either anincoming or outgoing trunk connection for establisliing an auxiliaryconnection to another branch-exchange subscriber from which connectionthe main-exchange subscriber is excluded, and means responsive tofurther directive impulses transmitted by the branchexchange subscriberfor releasing said auxiliary connection and for reestablishing` thetrunk connection.

24. In a telephone system, a trunk line having two branches adapted tobe connected to the trunk line alternately, means for transmittingseries of digit impulses over the trunk line to establish separateconnections t0 called lines over said branches, and an auxiliary switchoperated one step for each series of impulses transmitted over the trunkline for controlling the connection of said branches to the trunk line.

25. In a telephone system, a trunk line hav-` ing two branches adaptedto be connected up one at a time, means for transmitting groups of digitimpulses over the trunk line,'each of said groups representing thedigits of a called-subscribers `number followed by an additional digit,means for repeating the called-number digits over the particular branchconnected, an auxiliary switch operated one step for each digittransmitted over the trunk line, and means controlled by the switch onoperating in response to the additional digit impulses for connecting upthe previously-disconnected branch. i

26. In a telephone system, a trunk line having two branches, automaticswitches, a line relay controlled over the trunk line for repeatingdigit impulses over one of said branches to operate certain of saidswitches to extend a connection to a called line, an auxiliary switchoperated one step responsive to each series of impulses representing adigit of acalled number, and means controlled by said switch whenoperated to a predetermined position Jfor adapting said relay to repeatiinpulses over the other .of said branches to operate certain other ofsaid automatic switches transmitting digit impulses over the trunk lineto complete outgoing calls to called subscribers, means for extendingincoming calls over the trunk line to subscribers in the e branchexchange, an auxiliary switch associated with the trunk line, a speakingposition for said switch to which the wipers of the switch are advancedone step at a time responsive to successive digits transmitted over thetrunk line to complete an outgoing call, and circuit connections forautomatically advancing the wipers of the switch to speaking position orincoming calls over the trunk line.

28. In a telephone system, a trunk line terminating in a branchexchange, means for transmtiting digit impulses over the trunk line tocomplete outgoing calls to called subscribers, means for extendingincoming calls over the trunk line to subscribers in the branchexchange, an auxiliary switch associated with the trunk line, a homeposition in which the wipers of the switch normally stand, a speakingposition to which the wipers of the switch are advanced one step at a.time in response to the digits of a called number on outgoing calls,circuit connections for automatically advancing the wipers of the switchto speaking position on incoming calls, and circuit connections forreturning the wipers of the switch to home position responsive to thetermination of either an outgoing or an incoming call.

In witness whereof, I hereunto subscribe my name this 19th `day ofSeptember, A. D.

HANS TATZL.

